1. Technical Field Text
Embodiments of the invention are directed to flexible tensioning members for a crane system and more particularly to a flexible crane tensioning member and connection assemblies.
2. Background Information
Large cranes are typically transported to a job site over the highway for at least a portion of the journey to a job site. Because many countries, states or other geopolitical entities impose limitations on the weight of vehicles (sometimes on a per-axle basis) that can be driven on highways within their jurisdiction, a large crane is typically broken into smaller pieces for transport. Once delivered to the job site, the crane is assembled from the smaller pieces. Some cranes, often referred to as mobile hydraulic cranes, are mounted on multi-axle transport carriers and are designed to travel over the highway and be ready for use at the job site with minimal set-up activity. However, to reduce the number of axles, there is a considerable benefit in reducing the weight of the crane, or transporting parts of the crane on a separate carrier to the job site.
Large cranes typically use a bracing structure to strengthen components of a crane such as a boom, jib, and mast. For example, a crane's boom may not be strong enough on its own to support the bending forces it is subject to when carrying a large load suspended from the tip of the boom. Rather than increase the cross section of the boom, which adds significantly to its weight, it is common to use a bracing structure to increase the stiffness and load capacity of the boom. The bracing structure typically includes at least one tensioning member under tension that extends from a location lateral of the boom to a location on the boom forming a triangle. The lateral location may be a strut coupled to the boom, or it may be a location offset from the boom on another structure of the crane.
In larger cranes the bracing structure itself may be relatively large and heavy. In some instances the bracing structure may require the use of another crane to lift it into place. In other instances, the bracing structure may be formed from smaller individual piecing connected together. These smaller individual pieces may be assembled in place on the crane, or assembled off of the crane and then attached to the crane as a single unit.
The individual pieces are typically formed from high tensile strength steel. In order for a worker to assembly the bracing structure, the individual pieces are typically no larger than a size that the workers can easily manipulate. Additionally, different cranes options may require different lengths of bracing structures or different strengths. For example, a boom may be extendable and require different lengths of bracing depending upon the extent that the boom is extended. For this reason a given crane configuration may have a specific set of bracing pieces associated with it.
FIG. 1 illustrates an example of a current tensioning member 100 made of high tensile strength steel. The tensioning member 100 is rigid with a high modulus of elasticity, such that any movement at one end of the tensioning member 100 is translated to the other end of the tensioning member 100. The tensioning member 100 may be joined end to end with another tensioning member to span a distance greater than a length 104 of the individual tensioning member 100. Tensioning member 100 has an eye 102 formed at one end of the tensioning member 100. The eye 102 is used to connect the tensioning member 100 to another component. For example, a pin may extend through the eye 102 and another component, fastening them together.
Because the tensioning member 100 is rigid, any movement between the tensioning member 100 and a crane must be accounted for. If the tensioning member 100 were rigidly attached to the crane, the tensioning member 100 would develop torsional loads in addition to a tension load and would likely experience a structural failure.
In some cranes the bracing structure may include steel cables as tensioning members. Steel cables are advantageous in some applications because they may be wound for storage and a single cable may be used to span a large distance. Additionally, steel cables are more forgiving in their attachment than sold cross section tensioning members 100 because they have some degree of flexibility. However, steel cables are typically not as strong as a solid cross section tensioning members 100 and therefore are not able to be used in all situations.
Tensioning members 100 and cables have been used successfully and continue to be used successfully in cranes. They are strong, readily available, and familiar to the operator. However, it would be beneficial to have a simpler system to replace the various combinations of tensioning members 100 and steel cables that offered similar strength while allowing for simple connection mechanisms.